Recently, large numbers of transmissions, for example, such an automatic transmissions for vehicles, which are capable of changing a reduction ratio in a multistep manner have already been developed, which are becoming established machines (for example, refer to Patent Document 1 and Non-Patent Document 1).
Patent Document 1: Japanese Published Unexamined Patent Application No. 2001-146964
Non-Patent Document 1: Edited by the Japan Society of Mechanical Engineers, “Mechanical Engineering Handbook, Design, β4: Machine Elements and Tribology,” First edition, published by the Japan Society of Mechanical Engineers, on 25 Oct. 2005, p. 83.